Turkish AKP government has stepped up arms supplies to Syrian jihadists to help them stave off an expected operation by the Syrian army in the northwest near the Turkish frontier, militant sources told Reuters news agency.

Senior militant officials told Reuters Turkish government had sent more military aid to jihadists in and around the Idlib region since a summit meeting with Iran and Russia last week failed to agree a deal to avert a government offensive into the area.

"They pledged complete Turkish military support for a long, protracted battle," a senior Free Syrian Army (FSA) commander who was privy to talks in recent days with senior Turkish officials told the agency, requesting anonymity as he was not authorised to speak publicly.

The weapons, which have entered Syria in large quantities in recent days, include ammunition and GRAD rockets, Reuters reported.

"These arms supplies and munitions will allow the battle to extend and ensure our supplies are not drained in a war of attrition," the commander added.

A second 'commander' said: "They are getting new shipments of munitions -- they don't need more than munitions."

The province in the northwest of Syria is the last remaining stronghold of armed groups in the country, including Nusra Front terrorist organization. Idlib's dominant terrorist faction is Tahrir al-Sham, a jihadist alliance spearheaded by al Qaeda's official affiliate in Syria, the Nusra Front.

The Turkish army has also deployed in the last week more troops and heavy weaponry to 12 positions in the Idlib region that observe a "de-escalation zone" agreed with Iran and Russia. The Turkish army has also sent troops into Syrian jihadist-held territory further east, in an area north of Aleppo city.

Turkish AKP government, which has backed some jihadists against the Syrian government, has previously said that a military operation into Idlib would be disastrous.

Tuesday's airstrikes came hours after U.S. President Donald Trump warned Syrian President Bashar al-Assad and his allies not to "recklessly attack" Idlib, saying that hundreds of thousands might die.